Many of the changes were small insertions that made his delivery more conversational. But others were lengthy passages that Clinton added at the last minute or improvised, from his praise of Republicans as “honorable people” to jokes about George Washington’s wooden teeth and Paul Ryan’s “brass.”

Clinton is regarded as one of the best political orators of his generation, but he is also known for walking a fine line between being memorable and being memorably long. In delivering the nominating speech for Michael S. Dukakis at the 1988 convention, Clinton famously drew mock applause when he uttered the phrase “in conclusion” at the end of his longwinded speech.

On Wednesday, Clinton’s improvisation pushed him well over his allotted time. Yet some of his wittiest and most impassioned moments — the ones that earned him near-universal praise — were unscripted. When he credited President Obama with setting the country on the right economic course and assured voters that “if you will renew the president’s contract, you will feel it,” Clinton added a personal message.

“Folks, whether the American people believe what I just said or not may be the whole election,” he said. “I just want you to know that I believe it. With all my heart, I believe it.”

In another improvisation, Clinton declared “this is personal to me” as he sought to debunk the Romney campaign’s charge that Obama has removed the work requirement in the 1996 welfare reform law — a law Clinton signed.

“Now, did I make myself clear? The requirement was for more work, not less,” Clinton said, defending Obama’s granting of waivers to states to experiment with new strategies to return 20 percent more welfare recipients to the workforce.

Clinton also embellished a section in which he praised Obama for appointing Clinton’s wife, Hillary — Obama’s chief rival in the Democratic primary — as secretary of state.

“I’m grateful for the relationship of respect and partnership she and the president have enjoyed and the signal that sends to the rest of the world, that democracy does not have to be a blood sport,” Clinton said. “It can be an honorable enterprise that advances the public interest.”

Talking about the GOP, Clinton delivered compliments and jabs on the spot. While alleging that the Republican Party has shifted to the right, Clinton added examples.

“Just in the last couple of elections, they defeated two distinguished Republican senators because they dared to cooperate with Democrats on issues important to the future of the country, even national security,” Clinton said, apparently referencing Dick Lugar of Indiana and Bob Bennett of Utah. “They beat a Republican congressman with almost 100 percent voting record on every conservative score because he said he realized he did not have to hate the president to disagree with him,” Clinton added, referring to Bob Inglis of South Carolina.

Clinton teased Ryan, the Republican vice presidential nominee, for blasting Obama’s $716 billion Medicare spending cut, noting Ryan included the cut in his budget proposal, which the House passed in the spring.

“You got to give one thing: It takes some brass to attack a guy for doing what you did,” Clinton said in an off-the-cuff wisecrack.

“People have predicted our demise ever since George Washington was criticized for being a mediocre surveyor with a bad set of wooden, false teeth,” Clinton said. “And so far every single person that’s bet against America has lost money because we always come back.”

Clinton is planning to build on his message next week by stumping for Obama in the two biggest swing states, Florida and Ohio.